The IBM developerWorks site has created a huge "recommended reading list" of artcles/tutorials/packages/etc for PHP developers of all skill levels to check out.
This list of recommended reading material on PHP is compiled from a variety of online sources by Web application developers in IBM's Global Production Services organization. These resources have been selected with the intention of introducing IT specialists and architects to PHP, providing specific information about development and maintenance, and helping to integrate the technology with IBM products.
They have the list broken up onto sections like "Development", "Community and News", and "Migration" with several sub-sections under each. Obviously, there are many more resources out there than just what's on this list, but it's a great start for anyone that really wants a crash course in all things PHP.